The White House may want to defuse its spat with the Chamber of Commerce, but Big Labor clearly has no such intentions.

Anna Burger, secretary-treasurer of the Service Employees International Union and chairwoman of the five-union federation Change to Win, slammed the big business lobby and its president, Tom Donohue, in a letter delivered today to House Financial Services Chairman Barney Frank and Rep. Spencer Bachus, the ranking Republican on the committee.

Accusing the Chamber of attacking “corporate reform,” Burger urged the lawmakers to reject several Chamber-backed amendments to legislation designed to strengthen investor protections, which is before the committee this week.

“You should not be misled by Mr. Donohue and the Chamber of Commerce into believing that such investor protections somehow undermine our nation’s economic position,” Burger said. “Mr. Donohue and the Chamber simply are not credible defenders of investor interests, and you should not treat their recommendations as anything but the attempt by a special interest to protect its privileged position.”

The amendments in question would modify section 404 of the Sarbanes-Oxley Act, the most controversial and costly provision of the law passed in the wake of corporate accounting scandals at Enron and other companies.

Burger said these amendments would weaken the much-needed protections provided by section 404, which requires publicly traded companies to maintain internal controls on their financial reporting, including documenting that the controls meet a certain standard of effectiveness.

“The investor protections provided by [the investor protection bill] and those already put in place seven years ago by Sarbanes-Oxley are vital to restoring confidence in the U.S. financial markets, and thereby ensuring recovery from the economic crisis of the past two years,” Burger said

Burger also used her letter to highlight Change to Win’s report on Donohue, which, Burger said, reveals a record of “questionable conduct and poor decision-making as a corporate director and that companies on whose boards he has served have … been victims of alleged insider trading, apparent stock options backdating, accounting scandals and substantial shareholder losses.”